PRINCIPLES OF BACKFLOW PREVENTION

Understanding the backflow prevention terminology is the key to knowing which backflow assembly is appropriate for a given installation. Backflow prevention assemblies are life safety products. If the wrong assembly is specified, the end result can be disastrous.

What Is Backflow?

Backflow is the undesirable reversal of the flow of a possible source of contamination (water or mixture of water and other liquids, gases, or other substances) into the potable water system.

 

When Does Backflow Occur?

Backflow is caused by pressure changes, including conditions of gravity, vacuum, or other pressure changes. There are two factors that contribute to reversal of flow in pipelines. One is backsiphonage and the other is backpressure.

Backsiphonage conditions exist when there is a negative or sub atmospheric pressure in the supply piping, allowing downstream substances to be siphoned into the potable water supply. Under-sized pipes, pipeline breaks, and high withdrawal rates can create vacuums, which contribute to the occurrence of backsiphonage. Backpressure conditions exist when a pressure higher than the supply is created in the downstream piping, allowing downstream substances to be pushed into the potable water supply. Backpressure can occur when higher pressures downstream are generated by pumps, thermal expansion, and elevation.

 

Selecting a Backflow Preventer

Zurn provides numerous types of backflow regulators/preventers to meet industry standards, which are set to provide the right level of protection depending on system conditions

Types of backflow preventers:

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Atmospheric Vacuum Breaker (AVB)

An AVB is a device containing a float-check, a check seat, and an air inlet port. The flow of water into the body causes the float to rise and close the air inlet port. When the flow of water stops, the float falls and forms a check valve against backsiphonage and, at the same time, opens the air inlet port to allow air to enter and satisfy the vacuum. A shut-off valve immediately upstream may be an integral component of the assembly.

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Pressure Vacuum Breaker (PVB)

A PVB is an assembly containing an independently acting, internally loaded check backflow valve with an independently acting loaded air inlet valve, located on the discharge side of the check valve. A PVB shall have two resilient-seated isolation valves attached at each end of the assembly and two properly located resilient seated test cocks.

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Spill Resistant Vacuum Breaker (SVB)

A SVB is the same as a Pressure Vaccum Breaker except that the Spill Resistant Vacuum Breaker is less prone to discharge upon fill, and is recommended for indoor installations. During start-up and operation, a separate diaphragm seals the air inlet from the water supply preventing spillage. The assembly is designed for use under constant pressure and 460XL provides protection where a potential health hazard exists.

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Dual Check backflow Valve and Dual Check with Atmospheric Port

Dual Checks are designed for use in low hazard applications where a fully approved, testable backflow preventer is not required. Check with the local authority having jurisdiction for acceptance.

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Double Check Valve Assembly (DC)

A DC is an assembly containing two independently acting approved check valves, four resilient-seated test cocks, and two resilient seated isolation valves.

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Double Check Detector Assembly (DCDA)

A DCDA is a specially designed assembly composed of a line sized approved double check backflow valve assembly, with a specific by-pass water meter, and a meter-sized approved double check valve assembly. The meter shall register accurately for all flows up to and including two gpm.

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Reduced Pressure Principle Assembly (RP)

A Reduced Pressure Principle Assembly(RP) is an assembly containing two independently acting approved check valves together with a hydraulically operated, mechanically independent differential pressure relief valve located between the two check valves.

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Backflow Preventer for Irrigation:

Zurn delivers industry leading water safety and water control solutions with our Zurn Wilkins irrigation backflow regulators & preventers. Developed with an emphasis on superior performance, customer value, and lowest lifecycle costs, Zurn Wilkins irrigation products are the smart solution – saving you time and money.

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300 Series Irrigation Backflow Preventer

The innovative 300 Series Small Backflow Preventer allows easy flushing upon installation to remove fouling debris that will fail the backflow prevention device, avoiding start-up delays and call backs. The 300 Series also allows contractors to quickly and easily winterize systems, resulting in increased productivity and customer satisfaction.

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Commercial Landscape Irrigation

The 375XLB Reduced Pressure Principle Backflow Preventer provides the ultimate backflow protection with a theft resistant design. The 375XLB Backflow uses less bronze, while the black fusion epoxy coating camouflages the bronze ball valves to virtually eliminate theft. In addition to theft deterrence, the 300 Series Backflow Peventer provides ease of maintenance with the removable EZSwap™ Pressure Vessel, providing simple line flushing and saving up to 15 minutes per installation. The EZSwap is removed and replaced with the Flush Fitting Tool in seconds, reducing repair costs and system down-time.

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Parks and Recreation

Zurn Wilkins 300 Series Winterizing Edition Backflow Preventer, which provides a backflow prevention device and blow-out accessory in a convenient, single package. The EZSwap™ Pressure Vessel is removed and replaced with the blow-out accessory in seconds to quickly and thoroughly winterize systems, preventing costly freeze damage. Faster winterization with the blow-out accessory increases productivity when the freeze is quickly approaching, saving time and money. The durable reinforced nylon pressure vessel resists corrosion and mineral build-up better than bronze.

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Agricultural Use

Zurn's innovative and proven design the 300AST Series corrosion resistant stainless steel body offers lower maintenance costs and a short lay length, allowing installation in tighter spaces. The proven and patented Compound Check provides reliable and secure check closure and low head loss. As agricultural backflow codes transition to testable Backflow Prevention Device from previous standards, Zurn Wilkins backflow preventers offer the required high-hazard protection.

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Residential Irrigation

Attractive landscaping is proven to add homeowner value. Landscaping for single and multi-family homes consists of small diameter lines for landscaping systems, including flower beds, lawns, trees, and water features. The 720A Pressure Vacuum Breaker is a time-tested design that delivers years of unparalleled service in high hazard backsiphonage conditions. When paired with the ZW3 Winterizer Valve Assembly and ZWFR Freeze Relief Valve, the 720A resists unexpected freeze damage and is easily winterized. The ZWFR is ideal where occasional/unexpected freezes occur and requires no periodic maintenance. The ZW3 allows winterization or maintenance to be performed by providing exterior access to an interior shut-off valve.

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